This application claims benefit of priority to Japanese Patent Application No. P10-292150 filed Oct. 14, 1998, the entire disclosure of which is incorporated by reference herein.
1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus for displaying a three dimension ultrasonic image obtained by scanning a three dimensional space with ultrasonic beams.
2. Discussion of the Background
Recently, there has been developed a real time three dimension diagnostic apparatus for displaying ultrasonic information of a three dimensional space in real time by scanning the three dimensional space with ultrasonic beams. In the field, there is utilized a technique of electronically scanning a three dimensional space with ultrasonic beams, simultaneously receiving signals in parallel, displaying information on an optional cross sectional surface or three dimension information and simultaneously collecting ultrasonic echo signals from a plurality of directions by receiving beams in a plurality of directions in response to one transmitted ultrasonic beam in order to scan a desirable space in real time.
However, it is necessary to provide a transmitted ultrasonic beam having a wide width to receive signals in parallel simultaneously so that deterioration of transmitting sensitivity can not be avoided. In fact, the size of each element in a two dimension array probe would become {fraction (1/30)} the size of each element in a conventional one dimension array probe. Therefore, the sound pressure of transmitted signals would be reduced and a S/N ratio of transmitting/receiving signals would be deteriorated.
The reduction of the sound pressure of the transmitting signals translates to a deterioration of the S/N ratio of a B-mode image (cross sectional image) and the problem of deteriorating color sensitivity becomes serious. Regarding a tissue harmonic mode and a contrast echo mode in which it is necessary to transmit signals at a sound pressure as high as possible, the reduction of the sound pressure is a serious problem. Regarding a real time three dimension ultrasonic diagnosis, it is required to have an image quality equal to or greater than that of a conventional B-mode ultrasonic diagnostic apparatus and to avoid deterioration of space analysis performance.
In the case of three dimension scanning in a parallel simultaneously receiving method, the directivity of elements, particularly in a sector type probe, has a adverse influence on the sensitivity of the apparatus.
In the conventional real time three dimensional ultrasonic diagnostic apparatus, a frame rate has been improved by widening a beam width of a transmitting beam and receiving echo signals from a plurality of directions simultaneously (number of simultaneously receiving signals transmitted in parallel is increased) in order to display a three dimensional image in real time by scanning a three dimensional space. Although the real time performance is improved by improving the frame rate, image quality is adversely influenced by deterioration of sensitivity, space analysis performance, the S/N ratio and a reduction of sound pressure. In the conventional parallel simultaneously receiving method, the sensitivity of a beam scanned in an oblique direction is more greatly deteriorated than that of a beam scanned in a direction perpendicular to an opening surface.
Accordingly, an object of the present invention is to provide an ultrasonic diagnostic apparatus for displaying in real time various ultrasonic information including a high quality cross sectional image based on cross sectional image data obtained by scanning a three dimensional space in real time.
Another object of the present invention is to provide an ultrasonic diagnostic apparatus which employs parallel simultaneous receiving, and in which sensitivity of a signal from a direction perpendicular to an aperture of a transducer and sensitivity of a signal from an oblique direction are substantially uniform.
These and other objects are achieved according to the present invention by providing a novel ultrasonic diagnostic apparatus for displaying ultrasonic information, wherein the ultrasonic information is obtained by scanning a three dimensional space with ultrasonic beams, and returned echo signals are subjected to parallel simultaneously receiving, including means for selecting a plurality of transmitting/receiving conditions wherein the number of signals simultaneously received in parallel is different in each condition, and means for switching at a desired period transmitting and receiving in the plurality of transmitting/receiving conditions, wherein various ultrasonic images are displayed based on ultrasonic information obtained from operation under the plurality of transmitting/receiving conditions.
In the above apparatus, a plurality of ultrasonic images of different quality can be displayed, while a three dimensional space is scanned in real time.
According to another aspect of the present invention, there is provided an ultrasonic diagnostic apparatus for scanning a three dimensional space with ultrasonic beams, receiving reflected echo signals and displaying ultrasonic information of the three dimensional space, including means for determining a first transmitting/receiving condition for scanning the whole three dimensional space and a second transmitting/receiving condition for scanning a specific region of the three dimensional space, means for alternately switching at a desired period transmitting and receiving between the first and second transmitting/receiving conditions, and means for displaying various ultrasonic images based on ultrasonic information obtained under the first and second transmitting/receiving conditions.
In the above apparatus according to the present invention, three dimensional image information can be obtained and displayed and fine image information of a predetermined region can also be obtained and displayed.
In an ultrasonic diagnostic apparatus according to the present invention as above described, the specific region scanned under the second transmitting/receiving condition is a cross sectional surface in an ultrasonic beam direction. Therefore, in the apparatus according to the present invention, three dimensional image information of an object and fine image information of a predetermined region of the object can be obtained and displayed.
According to a further aspect of the ultrasonic diagnostic apparatus according to the present invention, the first and second transmitting/receiving conditions can differ from each other in regard to at least one of sound pressure, a central frequency, bandwidth, and pulse cycles of a transmitted ultrasonic beam, an aperture size of transmission, transmitting focus point, a weighting function of a transmitting ultrasound on an aperture, and a central frequency and band of receiving ultrasonic beams, an aperture size at a receiving side, receiving focus point, a weighting function of a receiving ultrasound on an aperture, a raster density of transmitting/receiving signal and imaging modes (such as B mode, Doppler mode, and harmonic mode).
Therefore, a plurality of various images having different image quality can be obtained and displayed.
In one embodiment of the ultrasonic diagnostic apparatus according to the present invention as above described, the number of signals simultaneously received in parallel under the first transmitting/receiving condition is more than that in the second transmitting/receiving condition. Therefore, the whole three dimensional space can be properly scanned in real time under the first transmitting/receiving condition and a specific region can be finely scanned under the second transmitting/receiving condition. Furthermore, in this embodiment, a beam width of a transmitting beam in the second transmitting/receiving condition is narrower that in the first transmitting/receiving condition. Therefore, the specific region can be finely scanned under the second transmitting/receiving condition. Further, according to a further aspect of this embodiment, the second transmitting/receiving condition is a transmitting/receiving condition in a harmonic mode. Therefore, the second transmitting/receiving condition selects high sound pressure in order to improve a S/N ratio and image resolution. Alternatively, the second transmitting/receiving condition is a transmitting/receiving condition in a color Doppler mode. Therefore, the second transmitting/receiving condition selects high sound pressure in order to improve color sensitivity.
In another variation, the first transmitting/receiving condition is selected to have low sound pressure and the second transmitting/receiving condition is selected to have high sound pressure. Therefore, in the first transmitting/receiving condition, breaking of micro bubbles included in a contrast medium can be reduced to as little as possible. In the second transmitting/receiving condition, signals generated by breaking micro bubbles are effectively detected so that an image in a contrast echo mode can be obtained with high S/N ratio and high resolution, i.e., improved likelihood of detecting unusual or abnormal tissue.
In yet another embodiment of the ultrasonic diagnostic apparatus according to the present invention, the second transmitting/receiving condition is a multi transmitting method for transmitting ultrasonic beams toward the same direction at a plurality of times, with varying focus points.
Therefore, in the second transmitting/receiving condition, the specific region can be finely scanned at a short period.
According to another embodiment of the present invention, there is provided an ultrasonic diagnostic apparatus for scanning a three dimensional space with ultrasonic beams and obtaining ultrasonic information of the three dimensional space in the parallel simultaneously receiving method, wherein a scanning space of ultrasonic beams becomes narrower and/or the number of signals simultaneously received in parallel is decreased the farther a scanned point is away from a center line of the three dimensional space. Therefore, in this embodiment in obtaining ultrasound information, beam scanning in a central direction and beams scanning in an oblique direction have the same sensitivity.